1. Field of the Invention
This invention relates to a protectively coated metal part, and in particular to an electrical connector part having a long lasting protective coating selectively applied upon exposed surfaces to maximize corrosion protection while maintaining electrical conductivity on mated surfaces.
2. Description of Related Art
The most common light metal alloy currently used in electrical connectors is aluminum, finished by means of electroplating, electroless plating, anodizing, or conversion coating using existing commercially available technology to form conductive parts. Such conductive parts include shielding members and conductive shells for electrically shielding signal carrying contacts or components in the connector. Aluminum has a number of advantages in terms of weight, relative strength, manufacturability, cost, and conductivity when finished by the above-mentioned well-known techniques. Nevertheless, aluminum is subject to corrosion when exposed, which can severly limit the life of a connector subject to severe environmental conditions such as salt air, thus forcing the use of more expensive and difficult to handle alloy materials.
To overcome the problem of corrosion, and also to provide a non-conductive finish for user handled portions of a connector, it has previously been proposed to provide an overmolded plastic protective layer on the aluminum base material of a connector shell. Use of an overmolded protective layer can be effective against corrosion, but the initial investment required to implement the overmolding process, and the subsequent manufacturing costs, are relatively high in comparison with an all metal connector.
The present invention also offers a solution to the problem of corrosion, but at less cost and much greater ease of manufacture, by applying to a metal part a coating made of a chemically inert organic material, and in particular the type of material known as a "dry film lubricant," "solid film lubricant," or "lubricating paint." As the name implies, dry film lubricants have previously been used as lubricating coatings for metal parts because they adhere tenaciously to specific metals, and provide excellent friction reduction in cases where fluid lubricants cannot be used.
For example U.S. Pat. No. 4,684,192 discloses a protective coating made of a dry film lubricant made of graphite on an aluminum cam arm used for latching a connector part. Similarly, a number of publications, such as IBM Technical Disclosure Bulletin, Volume 15, No. 2; Soviet Patent publication No. 1062820; and U.S. Pat. Nos. 4,268,568, 4,355,124, and 3,620,839 all disclose dry film lubricants in the context of electrical switch contact lubrication.
However, in each of the above mentioned disclosures, the coatings are used on metal parts which contact other relatively moving metal parts, and not for protective purposes in situations where lubrication is not needed. In fact, it is very well-known to employ dry film lubricants as lubricants for purposes of friction reduction by applying the coatings to metal parts which contact and move relative to other metal parts. On the other hand, the advantages provided by using dry film lubricants as environmental sealants on parts which do not contact other parts has heretofore not been recognized. Use of dry film lubricants as corrosion protection coatings provides an entirely new class of connectors with all of the advantages of overmolded connectors and none of the disadvantages.